The present invention relates to analytical instruments for detecting and identifying low concentrations of selected air-borne vapors or particulates, and especially to portable instruments. The present invention has particular application to rapid detection and identification of trace air contaminants such as vapors of cocaine, heroin, explosives, radioactive substances, and other substances that may be carcinogenic, highly toxic, or of forensic interest. More specifically, the invention relates to portable high-throughput liquid-absorption air-sampling apparatus and methods.
Liquid-absorption sampling has been used successfully for the collection of many different analyte vapors, including those of trinitrotoluene, alkaloids, primary aromatic amines, hydrazines, hydrogen peroxide, nitrogen oxide, diisocyanates, 2-chloronitrobenzene, and several inorganic halogen compounds (HCl, HF, F.sub.2, and other hydrolyzable fluorides). Preferably, as disclosed in my U.S. Pat. No. 5,328,851, the extractant should react rapidly with the analyte to yield a product that can be measured electrochemically, preferably using a miniaturized amperometric or potentiometric sensor, or photometrically, e.g., colorimetrically or by chemiluminescence, using a built-in, preferably fiber-optic, detector. This should yield a portable yet highly sensitive, near real-time, self-contained analytical instrument. Alternatively, near real-time recording of sampled air compositions can be obtained by feeding the collected liquid into separate properly marked vials at predetermined intervals.
It is also recognized that many chemical compounds tend to be preferentially adsorbed onto solid surfaces, especially air-borne solid particulates, or absorbed by liquids, especially water droplets. This is true of most explosives and at least some propellants and chemical warfare agents. Therefore, suspended liquid and solid particulates may serve as natural pre-concentrators. It may be advantageous to collect analytes from air-borne water droplets and/or particulates. This advantage is not readily offered by alternative types of pre-concentrators.
U.S. Pat. No. 5,328,851 discloses an advanced high-throughput liquid-absorption pre-concentrator (HTLAP) which incorporates the pre-concentrating sampler of U.S. Pat. No. 4,977,095 and the analytical system of U.S. Pat. No. 4,942,135, and which further provides for rapid detection and analysis of air-borne contaminants that may be in form of vapor or contained in aerosols.
Also, as a continuation-in-part of co-pending application Ser. No. 08/377,966, this invention relates to apparatus and methods for monitoring the concentrations of hazardous substances contained in respirable particulates, especially lead in fire ranges, in and around lead-smelting or lead-fabricating facilities, lead-acid battery or pottery and ceramic plants, radiator repair and other soldering shops, dwellings contaminated with chipping lead paint, and other locations were elevated respirable levels may pose a hazard to human health.
It is therefore the purpose of this invention to provide a cost-effective method and instrumentation for monitoring airborne lead concentrations in said locations to help prevent lead poisoning among exposed persons.
In copending application Ser. No. 08/377,966, reference is made to a portable HTLAP device as one of two alternative means for collecting lead-containing particulates and solubilizing them in a liquid extractant. The present invention is addressed specifically to the realization of a portable HTLAP. The HTLAP that is disclosed in my U.S. Pat. No. 5,328,851 is a "transportable unit" which can not be easily carried single-handedly.
It is therefore another object of this invention to provide an inexpensive, portable, and rapid means for estimating airborne concentrations of lead or of other hazardous air contaminants using a portable high-throughput liquid-absorption air sampler [PHTLAAS].
The "transportable" HTLAP that is disclosed in U.S. Pat. No. 5,328,851 uses an elongated vertical tube with a wetted interior wall along whose surface a liquid film is caused to drain down by gravity. The vertical drainage is incompatible with efficient operation of the sampler at different orientations, especially those approaching the horizontal one. However, during inspections for illicit drugs or explosives, it may be necessary to insert the PHTLAAS into nooks, crannies or horizontal slots between closely stacked crates in order to pick up traces of hidden illicit substances.
It is therefore another object of the invention to provide methods of using the PHTLAAS as a probe that can be operated in any arbitrary orientation while still retaining a capability for picking up low concentrations of vapors or air-borne particulates.
The HTLAP that is disclosed in U.S. Pat. No. 5,328,851 requires that the sampled air not be exposed to unheated dry surfaces before coming in contact with a liquid absorbing film that is draining down its wetted interior wall. This requirement would make it difficult or impossible to operate the sampler at orientations that are highly inclined from the vertical direction.
It is therefore another object of this invention to provide methods of efficiently operating HTLAP and especially PHTLAAS devices without their interior wall being mostly wetted.
Previously reported high-throughput liquid-absorption air scrubbers, including the HTLAP that is disclosed in my U.S. Pat. No. 5,328,851, require an air suction of &gt;30 cm of water, possibly even &gt;100 cm of water, and consequently a heavy pump and a rather large power input for their operation. They also utilize a liquid-supply reservoir and a liquid-metering pump. These features are incompatible with compact and light-weight devices that can be conveniently hand-carried.
It is therefore still another object of this invention to provide a PHTLAAS that can operate without a liquid-metering pump, without a liquid reservoir or with a substantially inconspicuous reservoir, and at a relatively low suction that can be effected by a small and light-weight D.C.-powered fan.
The HTLAP that is disclosed in my U.S. Pat. No. 5,328,851 uses an aqueous liquid extractant that is not readily compatible with certain analytical instruments, such as a gas chromatograph [GC] or an ion mobility spectrometer [IMS].
It is therefore still another object of this invention to render the HTLAP, and especially the PHTLAAS, conveniently usable with GC, IMS, and other instruments that are not geared for analyzing aqueous samples.
Radio-active substances, such as tritium or tritiated water, are encountered in nuclear reactor facilities. It may be important to monitor the concentrations of such substances in air over short time intervals. It is therefore yet another object of this invention to provide methods of monitoring the concentrations of radioactive substances in air, especially of tritiated water, with the aid of a PHTLAAS.
Other objects of the invention will become apparent to professionals in the health monitoring, industrial safety and hygiene, environmental, metallurgical, forensic, and related areas following perusal of the complete specification.